The present invention herein resides in the art of defense systems for diverting the trajectory of incoming missiles. More particularly, the present invention relates to a system which provides simultaneous tracking and identification/classification functions with an infrared receiver having a focal plane array. Specifically, the present invention relates to a system which generates a laser beam to illuminate the missile and which provides variable imaging rates to detect, jam and divert an incoming infrared missile, wherein the system is enhanced by nulling the infrared receiver during generation of the laser beam.
To protect and defend military platforms, such as ships, aircraft, and ground-based installations, it is known to provide countermeasure systems that detect incoming threats such as enemy aircraft or missiles. Known systems detect incoming threats, such as infrared missiles, and then deploy defensive countermeasures in an attempt to destroy or divert the threat. These systems are referred to as open-loop systems since no immediate determination as to the type of threat or effectiveness of the countermeasure is readily available. Due to the inefficiency of the open-loop systems, closed-loop systems have been developed.
There are known performance benefits to using a directional, laser-based, closed-loop infrared countermeasure system to defeat infrared missiles. In a closed-loop system, the incoming missile is identified and the countermeasure system generates or tunes a jam code according to the specific incoming missile. The optimized jam code is directed at the missile which executes a maximum turn-away from its intended target. An additional feature of closed-loop techniques is the ability to monitor the classification and identification process during the jamming sequence. This provides a direct observation of the countermeasure effectiveness as well as an indication of the necessary corrective action required for the jam code. It will be appreciated that the benefits of the closed-loop performance system must be balanced against the cost of upgrading existing infrared directional countermeasure systems with a closed-loop capability, or against the cost of developing an entirely new closed-loop system.
One possible configuration for introducing a closed-loop receiver into a directional countermeasure system is to use a high resolution tracking sensor side-by-side with an infrared detector assembly. Accordingly, an independent receive channel, which is a separate optical path, must be added to the detection system with a separate expensive cooled detector. The cost and size impact of such a configuration to the countermeasure system is prohibitive.
Another approach is to incorporate an infrared detector assembly into the countermeasure system and split a portion of the received optical path for the high resolution tracking sensor. Unfortunately, this approach causes at least a 50% receive loss for both the track sensor and the receiver, plus the cost for adding another cryogenically cooled detector. Another problem with this approach is that the apertures of the sensor and the receiver may not match which would require a larger overall assembly to accommodate both.
Based upon the foregoing, it is apparent that there is a need in the art for a single imaging infrared receiver having a focal plane array capable of sufficient frame rates to provide sensor data for three primary closed-loop countermeasure functions. The receiver must have a passive high resolution tracking capability, it must be able to receive and process laser signals, and finally, the receiver must be able to perform countermeasure effectiveness measurements. Further, there is a need for the receiver to be nulled for a predetermine period of time so as to avoid interference from the laser signals.
In light of the foregoing, it is a first aspect of the present invention to provide a closed-loop infrared countermeasure system using a high frame rate infrared receiver with nulling sequence.
The foregoing and other aspects of the present invention, which shall become apparent as the detailed description proceeds, are achieved by a missile tracking and diverting system, comprising: a countermeasure processor for generating a trajectory signal of a detected missile; a track processor for receiving said trajectory signal and generating a pointer trajectory signal; a pointer for receiving said pointer trajectory signal to position said pointer toward the missile and track the trajectory of the detected missile; a laser positioned by said pointer; and an infrared receiver comprising an infrared focal plane array that integrally and simultaneously combines a tracking camera and a laser receiver, said infrared receiver positioned by said pointer; said countermeasure processor simultaneously generating an initiation signal and a blanking signal, said initiation signal causing said laser to generate a periodic pulsed signal that includes a laser pulse within a laser pulse interval, said blanking signal instructing said focal plane ray to initiate a hold-off time, which is longer than said laser pulse, prior to turning said infrared receiver on so as to allow for back scatter decay, said countermeasure processor generating a jam code for inclusion with said periodic pulsed signal to divert the trajectory of the detected missile.
Still other aspects of the present invention are achieved by a method for diverting the trajectory of a missile, comprising: analyzing characteristics of a detected missile with a countermeasure processor which generates a trajectory signal; processing said trajectory signal to generate a trajectory pointer signal; receiving said pointer signal in a pointer that follows the missile trajectory, said pointer positioning a laser and an infrared receiver which has a single focal plane array that integrally and simultaneously combines the functions of a tracking camera and a laser receiver; simultaneously generating an initiation signal and a blanking signal from said countermeasure processor; generating a sequence of periodic laser pulses that includes a laser pulse within a laser pulse interval from said laser upon receipt of said initiation signal; receiving said blanking signal in said infrared receiver; initiating a hold-off time of said focal plane array upon receipt of said blanking signal by said infrared receiver, prior to turning said infrared receiver on wherein said hold-off time is longer than said laser pulse so as to allow back scatter decay of said laser pulse; and generating a jam code by said counter-measure processor for inclusion with said laser pulse to divert the missile front its trajectory.